High-repetition low-peak-power frequency multiplication device and laser thereof

Abstract

The application discloses a high-repetition-frequency low-peak-value frequency doubling device and a laser thereof. The high-repetition-frequency low-peak-value frequency doubling device comprises a first module, a second module and a third module, the first module, the second module and the third module are sequentially arranged and constitute a frequency doubling module for guiding infrared pulse light input and outputting green pulse light; the laser comprises the high-repetition-frequency low-peak-value frequency doubling device; in the application, the frequency doubling efficiency of the infrared pulse light is improved through cooperation of the first module, the second module and the third module, the defect of low peak power of the fiber laser is sufficiently made up, and meanwhile the characteristic of high average power of the fiber laser is reserved.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and specifically to a high repetition rate, low peak value frequency doubling device and its laser. Background Technology

[0002] High repetition rate (e.g., 532 nm) green light plays a crucial role in cutting-edge fields such as laser marking, precision scanning, optical imaging, and medical diagnostics. Currently, the mainstream approach to generating this type of green light is based on frequency doubling technology (second harmonic generation), which uses a nonlinear crystal to convert the 1064 nm infrared pulses output from a fiber laser into green light. Fiber lasers, with their high stability, excellent beam quality, and ability to support high repetition rates, have become the core seed source for realizing high-frequency green light sources.

[0003] However, in practical applications, fiber lasers are limited by their small mode field diameter, and there are certain physical bottlenecks in improving their peak power.

[0004] Especially for narrow-linewidth lasers with pulse widths greater than 10 ns, the stimulated Brillouin scattering (SBS) effect further limits the upper limit of peak power. For example, under the influence of the SBS effect, the peak power of a laser with a core diameter of 20 μm can only reach about 0.13 kW, and even if the core diameter is increased to 40 μm, the peak power can only be increased to 0.53 kW. This low peak power characteristic directly leads to a dilemma in the subsequent nonlinear frequency conversion process: taking the commonly used LBO frequency doubling crystal as an example, if the ideal frequency doubling efficiency is to be obtained using the above weak peak power, the optical system must focus the spot to below 100 μm to significantly increase the power density, but this is very likely to cause the frequency doubling crystal to break down or be damaged.

[0005] In other words, existing technical solutions not only struggle to achieve high-efficiency conversion under low peak power conditions, thus limiting the output brightness and system performance of high-repetition-rate green light, but also fail to meet the industry's stringent requirements for high stability and high peak power due to the extremely high risk of damage to the frequency doubling crystal.

[0006] Therefore, how to overcome the shortcomings of the existing technology is the subject of this invention. Summary of the Invention

[0007] The purpose of this invention is to provide a high repetition rate, low peak value frequency doubling device and its laser.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high repetition rate, low peak value frequency multiplication device includes a first module, a second module, and a third module;

[0010] The first module, the second module, and the third module are sequentially configured to form a frequency doubling module for guiding the input of infrared pulse light and outputting green pulse light;

[0011] The first module serves as a pulse input terminal to guide an infrared pulse light with a repetition rate of N and a peak power of P into the frequency doubling module. In the infrared pulse light with a repetition rate of N, N is an even number. The first module is used to reduce the repetition rate and increase the peak power of the incident infrared pulse light with a repetition rate of N, thereby obtaining a repetition rate of N / (2π / 2π). f ), peak power is (2 f The first pulse of light P, where f represents the number of pulses;

[0012] The second module is positioned between the first and third modules and performs laser frequency doubling on the first pulse light to obtain the second pulse light;

[0013] The repetition rates of the second pulse and the first pulse are equal, and both are N / (2). f The peak power of the second pulse light is less than or equal to 0.8 × (2). f P;

[0014] The third module serves as a pulse output terminal, used to guide the second pulse light to perform repetition rate increase and peak power reduction actions to obtain and output the third pulse light;

[0015] The repetition frequency of the third pulse light is N, and the peak power is less than or equal to 0.8 × P;

[0016] Furthermore, both the second and third pulses are green pulses.

[0017] In the above scheme, the frequency doubling efficiency of infrared pulse light can be improved by the cooperation of the first module, the second module and the third module, which can fully make up for the low peak power of fiber lasers, while retaining the high average power of fiber lasers.

[0018] In a further technical solution, the first module includes a first half-wave plate, a photoelectric modulator, a first polarization beam splitter, a first roof prism, a first reflector, a second reflector, and a second polarization beam splitter.

[0019] The first ridge prism, the first reflector, and the second reflector constitute the first branch.

[0020] Along the input direction of the infrared pulse light, the first half-wave plate, the photoelectric modulator, the first polarization beam splitter, and the second polarization beam splitter are arranged in a straight line and spaced apart, and the first polarization beam splitter and the second polarization beam splitter are respectively located at both ends of the first branch.

[0021] The photoelectric modulator can change the polarization direction of infrared pulse light from vertical polarization to horizontal polarization;

[0022] In use, the photoelectric modulator is selectively turned on so that the infrared pulse light is split into a first infrared pulse beam with vertical polarization and a second infrared pulse beam with horizontal polarization.

[0023] The first polarization beam splitter directs the first infrared pulse beam and the second infrared pulse beam into the first branch and the second polarization beam splitter, respectively. The second polarization beam splitter combines each pulse from the first infrared pulse beam from the first branch and the first polarization beam splitter and each pulse from the second infrared pulse beam into a one-to-one beam to form the first pulse light.

[0024] With the above design, the first and second infrared pulse beams separated from the infrared pulse light can be combined into a beam with a polarization direction of 45 degrees and a repetition rate of N / (2). f ), peak power is (2 f The first pulse of light from P.

[0025] In a further technical solution, the first infrared pulse beam splitting is formed by multiple first pulses; the second infrared pulse beam splitting is formed by multiple second pulses.

[0026] There is a time delay between the first pulse and the second pulse, and this time delay is δ1;

[0027] In the first branch, the first ridge prism and the first reflector are spaced apart, and the distance between them is d1, where d1 = 1 / 2 × (c × δ1).

[0028] Where c is the speed of light.

[0029] With the above design, the time delay between the first pulse and the second pulse can be controlled by controlling the interval between the first ridge prism and the first reflector, so that the first pulse and the second pulse can be combined.

[0030] It should be noted that d1 is generally controlled within , It is the pulse duration.

[0031] In a further technical solution, on the first polarization beam splitter, with a plane that faces and is perpendicular to the input direction of the infrared pulse light as a reference, the polarization directions of the first pulse and the second pulse are perpendicular to each other.

[0032] With the above design, the first pulse and the second pulse can satisfy the orthogonal polarization beam combining condition at the second polarization beam splitter, ensuring maximum energy superposition efficiency and stable and controllable phase relationship.

[0033] In a further technical solution, the second module includes a second half-wave plate, a beam shaping module, a frequency doubling crystal, a first filter, a light collecting plate, and a second filter;

[0034] Along the input direction of the infrared pulse light, the second half-wave plate, the beam shaping module, the frequency doubling crystal, the first filter, and the light collecting plate are arranged in a straight line and spaced apart.

[0035] The frequency doubling crystal is used to double the first pulse light and split it into a first beam and a second beam. In use, both the first beam and the second beam are output to the first filter. The second beam is reflected by the first filter to the second filter. The first beam passes through the first filter and is transmitted to the light collector.

[0036] With the above design, the input infrared pulse light can be converted into a first pulse light and a second pulse light by a frequency doubling crystal. Then, the first filter separates the first pulse light and the second pulse light. The light collector collects the first pulse light for subsequent detection, and the second filter performs secondary filtering on the reflected second pulse light to remove any possible residual frequency doubling components or other stray light, ensuring that the final output fundamental frequency signal has extremely high spectral purity.

[0037] In a further technical solution, the third module includes a third half-wave plate, a third polarizing beam splitter, a third reflecting mirror, a fourth reflecting mirror, a second roof prism, and a fourth polarizing beam splitter.

[0038] The third reflecting mirror, the fourth reflecting mirror, and the second roof prism constitute the second branch.

[0039] Along the direction of the second pulse light toward the input of the third module, the second filter, the third half-wave plate, the third polarizing beam splitter, and the fourth polarizing beam splitter are arranged in a straight line and spaced apart, and the third polarizing beam splitter and the fourth polarizing beam splitter are respectively located at both ends of the second branch.

[0040] The third polarization beam splitter is configured to split the second pulse light into a first green pulse beam and a second green pulse beam with equal peak power and perpendicular polarization directions, wherein the first green pulse beam is horizontally polarized and the second green pulse beam is vertically polarized.

[0041] In use, the first green pulse beam is split and transmitted to the fourth polarization beam splitter, and the second green pulse beam is split and transmitted to the second branch. The fourth polarization beam splitter combines the first green pulse beam and the second green pulse beam to form a third pulse beam.

[0042] With the above design, the first green pulse beam splitting and the second green pulse beam splitting can be made to coincide under orthogonal polarization states, ensuring that the third pulse light after beam combining has stable linear polarization characteristics and uniform energy distribution.

[0043] In a further technical solution, the first green pulse beam is formed by multiple third pulses;

[0044] The second green pulse spectral split is formed by multiple fourth pulses;

[0045] There is a time delay between the third pulse and the fourth pulse, and this time delay is δ2;

[0046] In the second branch, the second ridge prism and the fourth reflecting mirror are spaced apart, and the distance between them is d2, where d2 = 1 / 2 × (c × δ2).

[0047] Where c is the speed of light.

[0048] The control range of d2 is d2 = 0.5 × c × δ2 ± 0.5 × c × , It is the pulse duration.

[0049] With the above design, the time delay between the third pulse and the fourth pulse can be controlled by adjusting the interval between the second ridge prism and the fourth reflector, so that the third pulse and the fourth pulse can be combined.

[0050] In a further technical solution, the second branch is configured to guide the second green pulse beam splitter to the fourth polarization beam splitter and the first green pulse beam splitter to achieve an overlapping state with equal time delay.

[0051] With the above design, the third and fourth pulses are precisely synchronized at the fourth polarization beam splitter to complete the beam combining operation.

[0052] The present invention also provides a laser including a high repetition rate (PRR) low peak value (LPV) frequency doubling device; the PPR frequency doubling device is configured to perform a PPR frequency doubling method; the PPR frequency doubling method includes:

[0053] Step 1: Sort the pulses in the infrared pulse light with a repetition rate of N in order;

[0054] Among them, the pulses in the infrared pulse light with a repetition frequency of N are 1, 2, 3, 4, 5, 6, ... N;

[0055] Step 2: Arrange the pulses in the infrared pulse light with a repetition frequency of N in an odd and even order. Use a first half-wave plate to convert all the pulses in the infrared pulse light with a repetition frequency of N into vertical polarization. Then, select only the pulses in the even-numbered sequence to pass through the photoelectric modulator, turn on the photoelectric modulator, so as to form a first infrared pulse beam split with vertical polarization and a second infrared pulse beam split with horizontal polarization.

[0056] In the first infrared pulse beam splitting, all pulses are sequentially 1, 3, 5, 7...N-1, and in the second infrared pulse beam splitting, the pulses are 2, 4, 6, 8...N;

[0057] Step 3: The first infrared pulse beam is split and reflected by the first polarization beam splitter to the first branch composed of the first roof prism, the first reflector and the second reflector, and the second infrared pulse beam is split and guided to the second polarization beam splitter by the first polarization beam splitter.

[0058] Step 4: Control the interval between the first roof prism and the first reflector to control the time delay of the first infrared pulse beam splitting, so that each pulse in the first infrared pulse beam splitting and each pulse in the second infrared pulse beam splitting that arrive at the second polarization beam splitter are combined one-to-one to form the first pulse light.

[0059] Step 5: The first pulse light passes sequentially through the second half-wave plate and the beam shaping module, so that the polarization direction and spot size of the first pulse light are adjusted to the orientation and set size required by the phase matching condition of the frequency doubling crystal;

[0060] Step 6: The first pulse light passes through the frequency doubling crystal and is split into a first pulse light and a second pulse light. The first pulse light passes through the first filter and is transmitted to the light collector. The second pulse light is reflected by the first filter to the second filter.

[0061] Step 7: The second pulse light is converted into linearly polarized light with a polarization angle of 45 degrees by the third half-wave plate, and then split into a first green pulse beam splitter and a second green pulse beam splitter with equal peak power and perpendicular polarization directions by the third polarization beam splitter. The first green pulse beam splitter is horizontally polarized and the second green pulse beam splitter is vertically polarized.

[0062] Step 8: The first green pulse beam is split and transmitted to the fourth polarization beam splitter, and the second green pulse beam is split and transmitted to the second branch consisting of the third mirror, the fourth mirror, and the second roof prism.

[0063] Step 9: Control the spacing between the fourth reflector and the second roof prism to control the time delay of the second green pulse beam splitting, so that the first green pulse beam splitting and the second green pulse beam splitting arriving at the fourth polarization beam splitter can be combined to form a high repetition rate third pulse light and output it.

[0064] The first module of the high repetition rate low peak value frequency doubling device includes a first half-wave plate, a photoelectric modulator, a first polarization beam splitter, a first roof prism, a first reflector, a second reflector, and a second polarization beam splitter.

[0065] The second module of the high repetition rate low peak value frequency doubling device includes a second half-wave plate, a beam shaping module, a frequency doubling crystal, a first filter, a light collector, and a second filter;

[0066] The third module of the high repetition rate low peak value frequency doubling device includes a third half-wave plate, a third polarization beam splitter, a third mirror, a fourth mirror, a second roof prism, and a fourth polarization beam splitter.

[0067] In the above scheme, high repetition rate green light can be obtained through the cooperation of the first module, the second module and the third module. This is different from the existing technology where fiber lasers have limited peak power due to their small mode field diameter, especially narrow linewidth lasers with pulse widths of more than 10ns. The peak power is affected by the SBS (stimulated Brillouin effect). The peak power of a 20um fiber core diameter can only reach 0.13kW, and that of a 40um fiber core diameter can only reach 0.53kW. Using fundamental frequency light with such peak power for frequency doubling, taking the commonly used LBO frequency doubling crystal as an example, the light spot needs to be focused to below 100um to achieve ideal frequency doubling efficiency. However, this operation is prone to damaging the frequency doubling crystal. In this invention, by reducing the repetition rate and increasing the peak power through the first module, the pulses in the infrared pulse light are made into a first pulse light with reduced repetition rate and increased peak power. Then, after frequency doubling and polarization control by the second module, a first light and a second pulse light are obtained. The first light passes through the first filter and is transmitted to the light collector. The second pulse light is transmitted to the third module. Subsequently, the third module will perform polarization rotation and beam splitting control on the second pulse light to generate two polarization orthogonal and power-equal green pulse beam splitters (i.e., the first green pulse beam splitter and the second green pulse beam splitter). By precisely adjusting the second branch to control the time delay of the second green pulse beam splitter, the first green pulse beam splitter and the second green pulse beam splitter that reach the fourth polarization beam splitter are combined to form a high repetition rate third pulse light and output a high-stability, high repetition rate, and high peak power third pulse light.

[0068] A further technical solution is to repeat steps seven through nine M times for the third pulse light, where M is a positive integer, in order to achieve repeated high-repetition-rate processing of the third pulse light.

[0069] With the above design, the third pulse light can achieve a higher repetition rate.

[0070] Due to the application of the above-mentioned solution, the technical solution of this application has the following advantages and effects compared with the prior art:

[0071] In this invention, the frequency doubling efficiency of infrared pulsed light can be improved by the cooperation of the first module, the second module and the third module, which fully makes up for the deficiency of low peak power of fiber lasers, while retaining the characteristic of high average power of fiber lasers.

[0072] Specifically, in use, an infrared pulse light with a repetition rate of N and a peak power of P is guided into a frequency doubling module composed of a first module, a second module, and a third module. At this time, the first module will reduce the repetition rate and increase the peak power of the injected infrared pulse light with a repetition rate of N to obtain a repetition rate of N / (2π / 2π). f ), peak power is (2 f The first pulse of light is P; subsequently, the second module performs laser frequency doubling on the first pulse of light to obtain a repetition rate of N / (2P). f Peak power less than or equal to 0.8 × (2) f The second pulse of light is generated by the third module, which then guides the second pulse of light to perform repetition rate increase and peak power reduction actions to obtain the third pulse of light and output it.

[0073] This invention, through the cooperation of the first, second, and third modules, can obtain high repetition rate green light. This differs from existing technologies where fiber lasers, due to their small mode field diameter, have limited peak power, especially narrow-linewidth lasers with pulse widths above 10 ns. The peak power is affected by the SBS (stimulated Brillouin effect), with a 20µm core diameter achieving only 0.13kW and a 40µm core diameter only 0.53kW. Using this fundamental frequency light with such peak power for frequency doubling, taking a commonly used LBO frequency doubling crystal as an example, the light spot needs to be focused below 100µm to achieve ideal frequency doubling efficiency. However, this operation is prone to damaging the frequency doubling crystal.

[0074] In this invention, by reducing the repetition rate and increasing the peak power of the first module, each pulse in the infrared pulse light is made into a first pulse light with reduced repetition rate and increased peak power. Then, after frequency doubling and polarization modulation by the second module, a first light and a second pulse light are obtained. The first light passes through the first filter and is transmitted to the light collector. The second pulse light is transmitted to the third module. Subsequently, the third module performs polarization rotation and beam splitting modulation on the second pulse light to generate two polarization orthogonal and power-equal green pulse beam splitters (i.e., the first green pulse beam splitter and the second green pulse beam splitter). By precisely adjusting the second branch to control the time delay of the second green pulse beam splitter, the first green pulse beam splitter and the second green pulse beam splitter that arrive at the fourth polarization beam splitter are combined to form a high repetition rate third pulse light and output a third pulse light with high stability, high repetition rate and high peak power. Attached Figure Description

[0075] Figure 1This is a schematic diagram of the first module, the second module, and the third module in an embodiment of the present invention.

[0076] In the above diagram: 1. First module; 11. First half-wave plate; 12. Photoelectric modulator; 13. First polarization beam splitter; 14. First roof prism; 15. First mirror; 16. Second mirror; 17. Second polarization beam splitter; 18. Infrared pulse light;

[0077] 111. First branch road;

[0078] 181. First infrared pulse spectral dispersion; 182. Second infrared pulse spectral dispersion;

[0079] 2. Second module; 21. Second half-wave plate; 22. Beam shaping module; 23. Frequency doubling crystal; 24. First filter; 25. Light collector; 26. Second filter;

[0080] 3. Third module; 31. Third half-wave plate; 32. Third polarization beam splitter; 33. Third mirror; 34. Fourth mirror; 35. Second roof prism; 36. Fourth polarization beam splitter;

[0081] 351. Second branch road;

[0082] 4. First pulse light; 41. Second pulse light; 42. First beam of light; 43. Third pulse light;

[0083] 411. First green pulse spectral dispersion; 412. Second green pulse spectral dispersion. Detailed Implementation

[0084] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0085] The terms "first," "second," etc., used in this article do not specifically refer to order or sequence, nor are they intended to limit this case; they are merely used to distinguish components or operations described using the same technical terms.

[0086] The terms "connection" or "positioning" as used in this article can refer to two or more components or devices making direct physical contact with each other, or making indirect physical contact with each other, or to two or more components or devices operating or moving with each other.

[0087] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0088] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0089] The terms “front,” “back,” “up,” “down,” “left,” and “right” used in this article are directional terms. In this case, they are only used to describe the positional relationship between the structures and are not intended to limit the specific direction of the protection scheme or its actual implementation.

[0090] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this work. Singular forms such as “a,” “this,” “this,” “the,” and “the” as used herein also include plural forms.

[0091] This application aims to solve the problem of how to effectively increase pulse peak power and optimize frequency doubling efficiency while maintaining high repetition rate characteristics.

[0092] See Figure 1 As shown, a high repetition rate and low peak value frequency multiplication device includes a first module 1, a second module 2 and a third module 3;

[0093] The first module 1, the second module 2, and the third module 3 are sequentially arranged and constitute a frequency doubling module for guiding the input of infrared pulse light 18 and outputting green pulse light;

[0094] In this module, the first module 1 serves as a pulse input terminal to guide an infrared pulse light 18 with a repetition rate of N and a peak power of P into the frequency doubling module. In the infrared pulse light 18 with a repetition rate of N, N is an even number. The first module 1 is used to reduce the repetition rate and increase the peak power of the injected infrared pulse light 18 with a repetition rate of N / (2π / P) to obtain a repetition rate of N / (2π / P). f ), peak power is (2 f The first pulse of P is 4, where f represents the number of pulses.

[0095] The second module 2 is located between the first module 1 and the third module 3, and performs laser frequency doubling on the first pulse light 4 to obtain the second pulse light 41;

[0096] Among them, the repetition rates of the second pulse light 41 and the first pulse light 4 are equal, and both are N / (2 f The peak power of the second pulse light 41 is less than or equal to 0.8 × (2). f P;

[0097] The third module 3 serves as a pulse output terminal, used to guide the second pulse light 41 to perform repetition rate increase and peak power reduction actions, so as to obtain the third pulse light 43 and output it.

[0098] Among them, the repetition rate of the third pulse light 43 is N, and the peak power is less than or equal to 0.8×P;

[0099] Furthermore, both the second pulse light 41 and the third pulse light 43 are green pulse lights.

[0100] In this invention, an infrared pulse light 18 with a repetition rate of N and a peak power of P is injected into the first module 1 once to obtain a first pulse light 4 with a repetition rate of N / 2 and a peak power of 2P. Injecting it twice yields a repetition rate of N / (2×2)P and a peak power of (2×2)P. Injecting it multiple times yields a repetition rate of N / (2×2)P. f ), peak power is (2 f )P.

[0101] In this invention, the first module 1 reduces the repetition rate, thereby increasing the pulse peak power; the second module 2 doubles the frequency, so it does not change the repetition rate, only reducing the peak power; the third module 3 is used to restore the repetition rate to the same N as before incident. In the third module 3, the power is the same as the light emitted from the second module 2, and the power remains unchanged. Therefore, the repetition rate becomes N, and the peak power is reduced accordingly.

[0102] Second module 2, output repetition frequency N / (2 f The third module 3 has an output repetition frequency N, and the second module 2 has a peak power less than or equal to 0.8 × (2 f Therefore, the peak output of the third module 3 is less than or equal to [N / (2P). f )]×[0.8×(2 f )P] / N=0.8×P.

[0103] In this invention, the frequency of the second pulse light 41 (i.e., the green pulse light) is equal to the frequency of the input infrared pulse (i.e., the first pulse light 4), both being N / (2 f Meanwhile, the peak power of the second pulse light 41 (i.e., the green pulse light) is positively correlated with the peak power of the infrared pulse (i.e., the first pulse light 4), which is why the peak power of the infrared pulse is increased first.

[0104] In this invention, the third module 3 can also combine vertically polarized and horizontally polarized pulsed light into one beam. For example, pulsed light one is vertically polarized and pulsed light two is horizontally polarized. By adjusting the delay of pulsed light one, pulsed light one and pulsed light two can overlap, and then the two pulses can become one pulsed light with a polarization direction of 45°.

[0105] In this invention, fiber lasers, especially narrow-linewidth lasers with pulse widths above 10 ns, suffer from limited peak power due to their small mode field diameter. Peak power is affected by the stimulated Brillouin effect (SBS), with a core diameter of 20 μm achieving only 0.13 kW and a core diameter of 40 μm achieving only 0.53 kW. Using this type of fundamental frequency light for frequency doubling, taking the commonly used LBO frequency doubling crystal 23 as an example, the beam spot needs to be focused to below 100 μm to achieve ideal frequency doubling efficiency. However, this operation easily damages the frequency doubling crystal 23.

[0106] Using this scheme, the peak power can be increased by more than 1000 times, greatly expanding the spot size of the laser beam driven into the frequency doubling crystal 23 and improving the frequency doubling efficiency. Therefore, this scheme is suitable for frequency doubling of fiber lasers with high repetition rate and low peak power, and fiber lasers with repetition rates between 1 and 1000 MHz.

[0107] In this invention, the frequency doubling efficiency of infrared pulsed light 18 can be improved by the cooperation of the first module 1, the second module 2 and the third module 3, which fully makes up for the defect of low peak power of fiber laser, while retaining the characteristic of high average power of fiber laser.

[0108] Specifically, in use, an infrared pulse light 18 with a repetition rate of N and a peak power of P is guided into a frequency doubling module composed of a first module 1, a second module 2, and a third module 3. At this time, the first module 1 will reduce the repetition rate and increase the peak power of the injected infrared pulse light 18 with a repetition rate of N to obtain a repetition rate of N / (2π / 2π / 2). f ), peak power is (2 f The first pulse of light 4 is generated by the second module 2; subsequently, the second module 2 performs laser frequency doubling on the first pulse of light 4 to obtain a repetition rate of N / (2π). f Peak power less than or equal to 0.8 × (2) f The second pulse light 41 of P is then guided by the third module 3 to perform repetition rate increase and peak power reduction actions to obtain the third pulse light 43 and output it.

[0109] Preferably, the first module 1 includes a first half-wave plate 11, an optoelectronic modulator 12, a first polarizing beam splitter 13, a first roof prism 14, a first reflector 15, a second reflector 16, and a second polarizing beam splitter 17.

[0110] The first ridge prism 14, the first reflector 15 and the second reflector 16 constitute the first branch 111;

[0111] Along the input direction of the infrared pulse light 18, the first half-wave plate 11, the photoelectric modulator 12, the first polarization beam splitter 13 and the second polarization beam splitter 17 are arranged in a straight line and spaced apart, and the first polarization beam splitter 13 and the second polarization beam splitter 17 are respectively located at both ends of the first branch 111.

[0112] The photoelectric modulator 12 can change the polarization direction of the infrared pulse light 18 from vertical polarization to horizontal polarization;

[0113] In use, the photoelectric modulator 12 is selectively turned on so that the infrared pulse light 18 is divided into a first infrared pulse beam splitter 181 with vertical polarization and a second infrared pulse beam splitter 182 with horizontal polarization.

[0114] The first polarization beam splitter 13 directs the first infrared pulse beam splitter 181 and the second infrared pulse beam splitter 182 into the first branch 111 and the second polarization beam splitter 17, respectively. The second polarization beam splitter 17 combines each pulse from the first infrared pulse beam splitter 181 and the second infrared pulse beam splitter 182 from the first branch 111 and the first polarization beam splitter 13 into corresponding beams to form the first pulse light 4.

[0115] With the above design, the first infrared pulse beam 181 and the second infrared pulse beam 182 split from the infrared pulse light 18 can be combined into a beam with a polarization direction of 45 degrees and a repetition rate of N / (2). f ), peak power is (2 f The first pulse of P 4.

[0116] It is important to note that "the higher the peak power, the higher the frequency doubling efficiency is usually", especially at the same average power, the higher the peak power, the higher the frequency doubling efficiency.

[0117] This is the fundamental reason why most high-efficiency green and ultraviolet lasers currently tend to use high peak power pulses (Q-switching, mode-locking) to pump frequency-doubling crystals. In nonlinear crystals, the conversion efficiency η of the frequency doubling process is related to the peak power density (or peak intensity) of the fundamental frequency light. The following relationship exists:

[0118] Low-efficiency region (when the fundamental frequency light is not significantly depleted):

[0119] η ≈ constant × ;

[0120] Therefore, in this design, the function of the first module 1 is to increase the peak power of the incident light by reducing the repetition rate.

[0121] Module 2 is a common frequency multiplier module. Because the peak power is increased, the frequency multiplication efficiency of the second module is improved.

[0122] The function of the third module 3 is to restore the original reduced repetition frequency to the repetition frequency of the incident light.

[0123] Preferably, the first infrared pulse beam splitter 181 is formed by a plurality of first pulses; the second infrared pulse beam splitter 182 is formed by a plurality of second pulses;

[0124] There is a time delay between the first pulse and the second pulse, and this time delay is δ1;

[0125] In the first branch 111, the first ridge prism 14 and the first reflector 15 are spaced apart, and the distance between them is d1, where d1 = 1 / 2 × (c × δ1).

[0126] Where c is the speed of light.

[0127] It should be noted that d1 is generally controlled within , It is the pulse duration.

[0128] With the above design, the time delay between the first pulse and the second pulse can be controlled by controlling the interval between the first ridge prism 14 and the first reflector 15, so that the first pulse and the second pulse can be combined.

[0129] In a further technical solution, the polarization directions of the first pulse and the second pulse are perpendicular to each other, with the plane facing and perpendicular to the input direction of the infrared pulse light 18 as a reference on the first polarization beam splitter 13.

[0130] The first infrared pulse beam 181 and the second infrared pulse beam 182 formed after being split by the first polarization beam splitter 13 have polarization directions that are perpendicular to each other; wherein, the infrared pulse light 18 is input to the first polarization beam splitter 13 along the incident direction.

[0131] With the above design, the first pulse and the second pulse can satisfy the orthogonal polarization beam combining condition at the second polarization beam splitter 17, ensuring maximum energy superposition efficiency and stable and controllable phase relationship.

[0132] Preferably, the second module 2 includes a second half-wave plate 21, a beam shaping module 22, a frequency doubling crystal 23, a first filter 24, a light collecting plate 25, and a second filter 26;

[0133] Along the input direction of the infrared pulse light 18, the second half-wave plate 21, the beam shaping module 22, the frequency doubling crystal 23, the first filter 24, and the light collecting plate 25 are arranged in a straight line and spaced apart.

[0134] The frequency doubling crystal 23 is used to multiply the first pulse light 4 and divide it into a first light beam 42 and a second pulse light beam 41. In use, the first light beam 42 and the second pulse light beam 41 are both output to the first filter 24. The second pulse light beam 41 is reflected by the first filter 24 to the second filter 26. The first light beam 42 passes through the first filter 24 and is transmitted to the light collector 25.

[0135] With the above design, the input infrared pulse light 18 can be converted into a first light 42 and a second pulse light 41 by the frequency doubling crystal 23. Then, the first filter 24 separates the first light 42 and the second pulse light 41. The light collector 25 collects the first light 42 for subsequent detection, and the second filter 26 performs secondary filtering on the reflected second pulse light 41 to remove any possible residual frequency doubling components or other stray light, ensuring that the final output fundamental frequency signal has extremely high spectral purity.

[0136] Preferably, the third module 3 includes a third half-wave plate 31, a third polarizing beam splitter 32, a third mirror 33, a fourth mirror 34, a second roof prism 35, and a fourth polarizing beam splitter 36.

[0137] The third reflecting mirror 33, the fourth reflecting mirror 34, and the second roof prism 35 constitute the second branch 351.

[0138] Along the input direction of the second pulse light 41 toward the third module 3, the second filter 26, the third half-wave plate 31, the third polarizing beam splitter 32 and the fourth polarizing beam splitter 36 are arranged in a straight line and spaced apart, and the third polarizing beam splitter 32 and the fourth polarizing beam splitter 36 are respectively located at both ends of the second branch 351.

[0139] The third polarization beam splitter 32 is configured to split the second pulse light 41 into a first green pulse beam splitter 411 and a second green pulse beam splitter 412 with equal peak power and perpendicular polarization directions, wherein the first green pulse beam splitter 411 is horizontally polarized and the second green pulse beam splitter 412 is vertically polarized.

[0140] In use, the first green pulse beam splitter 411 is transmitted to the fourth polarization beam splitter 36, and the second green pulse beam splitter 412 is transmitted to the second branch 351. The fourth polarization beam splitter 36 combines the first green pulse beam splitter 411 and the second green pulse beam splitter 412 to form the third pulse beam 43.

[0141] With the above design, the first green pulse beam splitter 411 and the second green pulse beam splitter 412 can be made to coincide under orthogonal polarization states, ensuring that the third pulse beam 43 after beam combining has stable linear polarization characteristics and uniform energy distribution.

[0142] Preferably, the first green pulse beam splitter 411 is formed by a plurality of third pulses;

[0143] The second green pulse beam splitter 412 is formed by multiple fourth pulses;

[0144] There is a time delay between the third pulse and the fourth pulse, and this time delay is δ2;

[0145] In the second branch 351, the second ridge prism 35 and the fourth reflector 34 are spaced apart, and the distance between them is d2, where d2 = 1 / 2 × (c × δ2).

[0146] Where c is the speed of light.

[0147] The control range of d2 is d2 = 0.5 × c × δ2 ± 0.5 × c × , It is the pulse duration.

[0148] With the above design, the time delay between the third pulse and the fourth pulse can be controlled by adjusting the interval between the second ridge prism 35 and the fourth reflector 34, so that the third pulse and the fourth pulse can be combined.

[0149] Preferably, the second branch 351 is configured to guide the second green pulse beam splitter 412 to the fourth polarization beam splitter 36 and the first green pulse beam splitter 411 to achieve an overlapping state with equal time delay.

[0150] With the above design, the third pulse and the fourth pulse are precisely synchronized at the fourth polarization beam splitter 36 to complete the beam combining operation.

[0151] Specifically, the beam combining operation of the second green pulse splitter 412 and the first green pulse splitter 411 is as follows: the first green pulse splitter 411 is formed by multiple third pulses, and therefore, the multiple third pulses can be arranged in the form of 2, 4, 6, 8...; the second green pulse splitter 412 is formed by multiple fourth pulses, and therefore, the multiple fourth pulses can be arranged in the form of 1, 3, 5, 7... During operation (illustrated below), the fourth pulse arranged as 1 enters the second branch 351 (that is, the fourth pulse arranged as 1 will start from the first...). The third pulse, arranged in a 2-position, is directly injected into the fourth polarization beam splitter 36. The time of the fourth pulse, arranged in a 1-position, in the second branch 351 is controlled so that the fourth pulse, arranged in a 1-position, coincides with the third pulse, arranged in a 2-position, in the fourth polarization beam splitter 36 to complete the beam combining. (The subsequent arrangement of the third and fourth pulses can be repeated according to the above operation.)

[0152] The present invention also provides a laser including a high repetition rate low peak value frequency doubling device, the high repetition rate low peak value frequency doubling device being configured to perform a high repetition rate low peak value frequency doubling method;

[0153] High repetition rate, low peak value frequency doubling methods include:

[0154] Step 1: Sort the pulses in the infrared pulse light 18 with a repetition rate of N in order;

[0155] Among them, the pulses in the infrared pulse light 18 with a repetition frequency of N are 1, 2, 3, 4, 5, 6, ... N;

[0156] Step 2: Arrange the pulses in the infrared pulse light 18 with a repetition rate of N in an odd and even order. Use the first half-wave plate 11 to convert all the pulses in the infrared pulse light 18 with a repetition rate of N into vertical polarization. Then, select the even-numbered pulses to pass through the photoelectric modulator 12 and turn on the photoelectric modulator 12 to form a first infrared pulse beam splitter 181 with vertical polarization and a second infrared pulse beam splitter 182 with horizontal polarization.

[0157] In the first infrared pulse beam splitter 181, all pulses are sequentially 1, 3, 5, 7...N-1, and in the second infrared pulse beam splitter 182, the pulses are 2, 4, 6, 8...N;

[0158] Step 3: The first infrared pulse beam 181 is reflected by the first polarization beam splitter 13 to the first branch 111 composed of the first roof prism 14, the first reflector 15 and the second reflector 16, and the second infrared pulse beam 182 is guided to the second polarization beam splitter 17 by the first polarization beam splitter 13.

[0159] Step 4: Control the spacing between the first roof prism 14 and the first reflector 15 to control the time delay of the first infrared pulse beam splitter 181, so that each pulse in the first infrared pulse beam splitter 181 and each pulse in the second infrared pulse beam splitter 182 that arrive at the second polarization beam splitter 17 are combined one-to-one to form the first pulse light 4.

[0160] Step 5: The first pulse light 4 passes sequentially through the second half-wave plate 21 and the beam shaping module 22, so that the polarization direction and spot size of the first pulse light 4 are adjusted to the orientation and set size required by the phase matching condition of the frequency doubling crystal 23.

[0161] Step 6: The first pulse light 4 passes through the frequency doubling crystal 23 and is divided into the first light 42 and the second pulse light 41. The first light 42 passes through the first filter 24 and is transmitted to the light collector 25. The second pulse light 41 is reflected by the first filter 24 to the second filter 26.

[0162] Step 7: The second pulse light 41 is converted into linearly polarized light with a polarization angle of 45 degrees by the third half-wave plate 31, and then split into a first green pulse beam 411 and a second green pulse beam 412 with equal peak power and perpendicular polarization directions by the third polarization beam splitter 32. The first green pulse beam 411 is horizontally polarized and the second green pulse beam 412 is vertically polarized.

[0163] Step 8: The first green pulse beam splitter 411 is transmitted to the fourth polarization beam splitter 36, and the second green pulse beam splitter 412 is transmitted to the second branch 351 composed of the third reflector 33, the fourth reflector 34, and the second roof prism 35.

[0164] Step 9: Control the spacing between the fourth reflector 34 and the second roof prism 35 to control the time delay of the second green pulse beam splitter 412, so that the first green pulse beam splitter 411 and the second green pulse beam splitter 412 arriving at the fourth polarization beam splitter 36 are combined to form a high repetition rate third pulse beam 43 and output.

[0165] The first module 1 of the high repetition rate low peak value frequency doubling device includes a first half-wave plate 11, an optoelectronic modulator 12, a first polarization beam splitter 13, a first roof prism 14, a first reflector 15, a second reflector 16, and a second polarization beam splitter 17.

[0166] The second module 2 of the high repetition rate low peak value frequency doubling device includes a second half-wave plate 21, a beam shaping module 22, a frequency doubling crystal 23, a first filter 24, a light collecting plate 25, and a second filter 26;

[0167] The third module 3 of the high repetition rate low peak value frequency doubling device includes a third half-wave plate 31, a third polarization beam splitter 32, a third reflector 33, a fourth reflector 34, a second roof prism 35, and a fourth polarization beam splitter 36.

[0168] In this invention, high repetition rate green light can be obtained through the cooperation of the first module 1, the second module 2, and the third module 3. This differs from existing technologies where fiber lasers, due to their small mode field diameter, have limited peak power, especially narrow-linewidth lasers with pulse widths above 10ns. The peak power is affected by the SBS (stimulated Brillouin effect), with a 20µm core diameter achieving only 0.13kW and a 40µm core diameter only 0.53kW. Using such a high-power fundamental frequency light for frequency doubling, taking the commonly used LBO frequency doubling crystal 23 as an example, the light spot needs to be focused below 100µm to achieve ideal frequency doubling efficiency. However, this operation easily damages the frequency doubling crystal 23. In this invention, through the repetition rate reduction and peak power increase processing of the first module 1, the pulses in the infrared pulse light 18 are transformed into a first pulse light 4 with reduced repetition rate and increased peak power. Then, through frequency doubling and polarization modulation by the second module 2, a first beam 42 and a second pulse light 41 are obtained. The first beam 42 passes through the first filter 24 and is transmitted to the light collector 25. The second pulse light... The second pulse beam 41 is transmitted to the third module 3. The third module 3 then performs polarization rotation and beam splitting control on the second pulse beam 41 to generate two polarization-orthogonal, power-equal green pulse beams (i.e., the first green pulse beam 411 and the second green pulse beam 412). By precisely adjusting the second branch 351 to control the time delay of the second green pulse beam 412, the first green pulse beam 411 and the second green pulse beam 412 that arrive at the fourth polarization beam splitter 36 are combined to form a high repetition rate third pulse beam 43 and output a high-stability, high-repetition-rate, and high-peak-power third pulse beam 43.

[0169] The beam combining operation of the second green pulse beam splitter 412 and the first green pulse beam splitter 411 is as follows: The first green pulse beam splitter 411 is formed by multiple third pulses, and therefore, the multiple third pulses can be arranged in the form of 2468...; the second green pulse beam splitter 412 is formed by multiple fourth pulses, and therefore, the multiple fourth pulses can be arranged in the form of 1357... During operation, the following example illustrates that the fourth pulse arranged as 1 enters the second branch 351 (that is, the fourth pulse arranged as 1 will be injected from the third polarization beam splitter 32 into the second branch 351 composed of the third reflector 33, the fourth reflector 34, and the second roof prism 35, and finally enter the fourth polarization beam splitter 36), and the third pulse arranged as 2 is directly injected into the fourth polarization beam splitter 36. The time of the fourth pulse arranged as 1 in the second branch 351 is controlled so that the fourth pulse arranged as 1 and the third pulse arranged as 2 coincide in the fourth polarization beam splitter 36 to complete the beam combining.

[0170] In this invention, the first pulse light 4 can repeat steps one through four to double the peak power of the first pulse light 4 again and reduce the repetition rate again. Specifically, the repetition rate can be obtained as N / (2 f), peak power is (2 f The first pulse of P, 4, after repeating steps one through four, yields a repetition rate of N / (2). 2 ), peak power is (2 2 The first pulse of light 4 is P (because the first pulse of light 4 with a repetition frequency of N / 2 and a peak power of 2P is repeated in steps one through four. Therefore, after repetition, the repetition frequency and peak power will change. It should be noted that when repeating the operation, the polarization direction needs to be adjusted first before the second and third injections. The polarization direction adjusted here is the same as that of the first injection. Therefore, the second and third operations can repeat the first operation).

[0171] Preferably, the third pulse light 43 is repeated step seven to step nine M times, where M is a positive integer, to achieve repeated high-repetition-rate processing of the third pulse light 43.

[0172] With the above design, the third pulse light 43 can achieve a higher repetition rate.

[0173] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high repetition rate, low peak value frequency doubling device, characterized in that: It includes the first module (1), the second module (2), and the third module (3); The first module (1), the second module (2) and the third module (3) are sequentially set and constitute a frequency doubling module for guiding the input of infrared pulse light (18) and outputting green pulse light; The first module (1) serves as a pulse input terminal to guide an infrared pulse light (18) with a repetition frequency of N and a peak power of P into the frequency doubling module. In the infrared pulse light (18) with a repetition frequency of N, N is an even number. The first module (1) is used to reduce the repetition frequency and increase the peak power of the injected infrared pulse light (18) with a repetition frequency of N / (2π) to obtain a repetition frequency of N / (2π) P. f ), peak power is (2 f The first pulse of P (4), f represents the number of pulses; The second module (2) is located between the first module (1) and the third module (3), and performs laser frequency doubling on the first pulse light (4) to obtain the second pulse light (41). Among them, the repetition frequencies of the second pulse light (41) and the first pulse light (4) are equal, and both are N / (2 f The peak power of the second pulse (41) is less than or equal to 0.8 × (2). f P; The third module (3) serves as a pulse output terminal, used to guide the second pulse light (41) to perform repetition rate increase and peak power reduction actions to obtain the third pulse light (43) and output it. Among them, the repetition frequency of the third pulse light (43) is N, and the peak power is less than or equal to 0.8×P; Furthermore, both the second pulse (41) and the third pulse (43) are green pulses; The first module (1) includes a first half-wave plate (11), a photoelectric modulator (12), a first polarization beam splitter (13), a first roof prism (14), a first reflector (15), a second reflector (16), and a second polarization beam splitter (17). Among them, the first ridge prism (14), the first reflector (15) and the second reflector (16) constitute the first branch (111). The second module (2) includes a second half-wave plate (21), a beam shaping module (22), a frequency doubling crystal (23), a first filter (24), a light collector (25), and a second filter (26). Along the input direction of the infrared pulse light (18), the second half-wave plate (21), the beam shaping module (22), the frequency doubling crystal (23), the first filter (24), and the light collecting plate (25) are arranged in a straight line and spaced apart; The third module (3) includes a third half-wave plate (31), a third polarizing beam splitter (32), a third mirror (33), a fourth mirror (34), a second roof prism (35), and a fourth polarizing beam splitter (36). Among them, the third reflector (33), the fourth reflector (34), and the second roof prism (35) constitute the second branch (351).

2. The high repetition rate, low peak value frequency multiplication device according to claim 1, characterized in that: Along the input direction of the infrared pulse light (18), the first half-wave plate (11), the photoelectric modulator (12), the first polarization beam splitter (13) and the second polarization beam splitter (17) are arranged in a straight line and spaced apart, and the first polarization beam splitter (13) and the second polarization beam splitter (17) are respectively located at both ends of the first branch (111). The photoelectric modulator (12) can change the polarization direction of the infrared pulse light (18) from vertical polarization to horizontal polarization; In use, the photoelectric modulator (12) is selectively turned on so that the infrared pulse light (18) is split into a first infrared pulse beam splitter (181) with vertical polarization and a second infrared pulse beam splitter (182) with horizontal polarization. The first polarization beam splitter (13) directs the first infrared pulse beam splitter (181) and the second infrared pulse beam splitter (182) into the first branch (111) and the second polarization beam splitter (17), respectively. The second polarization beam splitter (17) combines each pulse from the first infrared pulse beam splitter (181) and the second infrared pulse beam splitter (182) from the first branch (111) and the first polarization beam splitter (13) into corresponding beams to form the first pulse light (4).

3. The high repetition rate, low peak value frequency multiplication device according to claim 2, characterized in that: The first infrared pulse beam splitter (181) is formed by a plurality of first pulses; the second infrared pulse beam splitter (182) is formed by a plurality of second pulses; There is a time delay between the first pulse and the second pulse, and this time delay is δ1; In the first branch (111), the first ridge prism (14) and the first reflector (15) are spaced apart, and the distance between them is d1, d1=1 / 2×(c×δ1). Where c is the speed of light.

4. The high repetition rate, low peak value frequency multiplication device according to claim 2, characterized in that: On the first polarization beam splitter (13), with a plane that faces and is perpendicular to the input direction of the infrared pulse light (18) as a reference, the polarization directions of the first pulse and the second pulse are perpendicular to each other.

5. The high repetition rate, low peak value frequency multiplication device according to claim 1, characterized in that: The frequency doubling crystal (23) is used to double the first pulse light (4) and divide it into a first light (42) and a second pulse light (41). When in use, the first light (42) and the second pulse light (41) are both output to the first filter (24). The second pulse light (41) is reflected by the first filter (24) to the second filter (26). The first light (42) passes through the first filter (24) and is transmitted to the light collector (25).

6. The high repetition rate, low peak value frequency multiplication device according to claim 5, characterized in that: Along the second pulse light (41) toward the input direction of the third module (3), the second filter (26), the third half-wave plate (31), the third polarization beam splitter (32) and the fourth polarization beam splitter (36) are arranged in a straight line and spaced apart, and the third polarization beam splitter (32) and the fourth polarization beam splitter (36) are respectively located at both ends of the second branch (351); The third polarization beam splitter (32) is configured to split the second pulse light (41) into a first green pulse beam splitter (411) and a second green pulse beam splitter (412) with equal peak power and perpendicular polarization directions, wherein the first green pulse beam splitter (411) is horizontally polarized and the second green pulse beam splitter (412) is vertically polarized. In use, the first green pulse beam splitter (411) is transmitted to the fourth polarization beam splitter (36), and the second green pulse beam splitter (412) is transmitted to the second branch (351). The fourth polarization beam splitter (36) combines the first green pulse beam splitter (411) and the second green pulse beam splitter (412) to form a third pulse beam (43).

7. The high repetition rate, low peak value frequency multiplication device according to claim 6, characterized in that: The first green pulse beam splitting (411) is formed by multiple third pulses; The second green pulse beam splitting (412) is formed by multiple fourth pulses; There is a time delay between the third pulse and the fourth pulse, and this time delay is δ2; In the second branch (351), the second ridge prism (35) and the fourth reflector (34) are spaced apart, and the distance between them is d2, d2=1 / 2×(c×δ2). Where c is the speed of light.

8. The high repetition rate, low peak value frequency multiplication device according to claim 6, characterized in that: The second branch (351) is configured to guide the second green pulse beam splitter (412) to the fourth polarization beam splitter (36) and the first green pulse beam splitter (411) to achieve an overlap state with equal time delay.

9. A laser, characterized in that: Includes the high repetition rate, low peak value frequency doubling device as described in any one of claims 1-8; The high repetition rate low peak value frequency multiplication device is configured to perform a high repetition rate low peak value frequency multiplication method; High repetition rate, low peak value frequency doubling methods include: Step 1: Sort the pulses in the infrared pulse light (18) with a repetition rate of N in order; Among them, the pulses in the infrared pulse light (18) with a repetition frequency of N are 1, 2, 3, 4, 5, 6, ... N; Step 2: Arrange the pulses in the infrared pulse light (18) with a repetition frequency of N in an odd and even order. Use the first half-wave plate (11) to convert all the pulses in the infrared pulse light (18) with a repetition frequency of N into vertical polarization. Then, select the even-numbered pulses to pass through the photoelectric modulator (12) to turn on the photoelectric modulator (12) to form a first infrared pulse beam splitter (181) with vertical polarization and a second infrared pulse beam splitter (182) with horizontal polarization. In the first infrared pulse beam splitter (181), all pulses are 1, 3, 5, 7...N-1 in sequence, and the pulses in the second infrared pulse beam splitter (182) are 2, 4, 6, 8...N; Step 3: The first infrared pulse beam (181) is reflected by the first polarization beam splitter (13) to the first branch (111) formed by the first roof prism (14), the first reflector (15) and the second reflector (16), and the second infrared pulse beam (182) is guided to the second polarization beam splitter (17) by the first polarization beam splitter (13). Step 4: Control the interval between the first roof prism (14) and the first reflector (15) to control the time delay of the first infrared pulse beam splitter (181), so that each pulse in the first infrared pulse beam splitter (181) and each pulse in the second infrared pulse beam splitter (182) that arrive at the second polarization beam splitter (17) are combined one-to-one to form the first pulse light (4). Step 5: The first pulse light (4) passes through the second half-wave plate (21) and the beam shaping module (22) in sequence, so that the polarization direction and spot size of the first pulse light (4) are adjusted to the orientation and set size required by the phase matching condition of the frequency doubling crystal (23); Step 6: The first pulse light (4) passes through the frequency doubling crystal (23) and is divided into the first light (42) and the second pulse light (41). The first light (42) passes through the first filter (24) and is transmitted to the light collector (25). The second pulse light (41) is reflected by the first filter (24) to the second filter (26). Step 7: The second pulse light (41) is converted into linearly polarized light with a polarization angle of 45 degrees by the third half-wave plate (31), and then split into a first green pulse beam splitter (411) and a second green pulse beam splitter (412) with equal peak power and perpendicular polarization directions by the third polarization beam splitter (32). The first green pulse beam splitter (411) is horizontally polarized and the second green pulse beam splitter (412) is vertically polarized. Step 8: The first green pulse beam splitter (411) is transmitted to the fourth polarization beam splitter (36), and the second green pulse beam splitter (412) is transmitted to the second branch (351) composed of the third mirror (33), the fourth mirror (34), and the second roof prism (35). Step 9: Control the spacing between the fourth reflector (34) and the second roof prism (35) to control the time delay of the second green pulse beam splitter (412), so that the first green pulse beam splitter (411) and the second green pulse beam splitter (412) arriving at the fourth polarization beam splitter (36) are combined to form a high repetition rate third pulse light (43) and output. The first module (1) of the high repetition rate low peak value frequency doubling device includes a first half-wave plate (11), an optoelectronic modulator (12), a first polarization beam splitter (13), a first roof prism (14), a first reflector (15), a second reflector (16), and a second polarization beam splitter (17). The second module (2) of the high repetition rate low peak value frequency doubling device includes a second half-wave plate (21), a beam shaping module (22), a frequency doubling crystal (23), a first filter (24), a light collector (25), and a second filter (26). The third module (3) of the high repetition rate low peak value frequency doubling device includes a third half-wave plate (31), a third polarization beam splitter (32), a third mirror (33), a fourth mirror (34), a second roof prism (35), and a fourth polarization beam splitter (36).

10. The laser according to claim 9, characterized in that: The third pulse light (43) repeats steps seven to nine M times, where M is a positive integer, to achieve repeated high-repetition-rate processing of the third pulse light (43).

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